Method of printing



United States Patent 3,0as,4ss METHOD OF PRINTING Erich A. Freund, 41026th Ave, San Francisco, Calif. No Drawing. Filed Aug. 11, 1960, Ser.No. 48,849 4 Claims. (43]. 101-426) This invention relates to a methodof letter press print- This application is a continuation-in-part of mycopending application Serial No. 544,060, filed October 31, 1955, nowabandoned.

In the method of this invention a printing medium such as printing inkis applied to a printing form and heated thereon at a temperature andfor a time sufficient to dry the medium on the form, that is, the mediumbecomes dry to the touch. The heated medium is then transferred from theform to a stock, such as paper and the like, by pressing the form andheated medium against the stock. Upon this pressing of the form andmedium against the stock, the dry medium is completely transferred fromthe form to the stock.

The principal feature of this invention therefore is to provide a methodof letter press printing in which the liquid printing medium is dried toa dry film condition on a form by heating and is then pressed againstthe stock while in this heated condition whereupon the dry medium iscompletely transferred from the form to the stock. Thus, the printingmethod of this invention is a dry method as contrasted to the ordinarywet method in which the fluid or plastic printing medium or ink isapplied to a form and then applied to the stock by pressing the coatedform against the stock while the medium is still in liquid or fluidcondition. Further, my new printing method involves a complete transferof the printing medium or ink onto the stock, in distinction to the meresplitting of an ink layer efiected in conventional printing.

Other features and advantages of the invention will be apparent from thefollowing description thereof taken in conjunction with representativeembodiments of the invention.

Any ordinary printing medium can be used in the practics of thisinvention so long as the medium is initially in a liquid or fluid stateand can be dried by heating to the dry film that is completely dry tothe touch, in other words, non-tacky. A vast number of different typesof printing media have been tested with the method of this inventionwithout failure, so long as they fulfill these requirements, that is, solong as they are initially liquid or fluid which includes thicksemi-plastic media and as long as they can be dried on a form to providean unbroken film that is dry to the touch and somewhat thermoplasticwhen subjected in heated condition to printing pressure. In commercialpractice it is preferred that the medium be driable at a temperature notlower than about 140 F. Similarly, for commercial printing, it ispreferred that the temperature required for drying be not over 350 F.primarily because of the added expense of maintaining such a hightemperature. On a commercial basis it is preferred that the printingmedium be driable to a dry film (that is, that it has no surface wetnessor tackiness) in not more than one minute. Actually, for practicalpurposes, this time which may be up to one minute should be not morethan a few seconds, such as 5 or 6 seconds and, preferably, a smallfraction of a second. The printin'g pressure that is employed inpressing the heated dry film against the stock can be the ordinaryprinting pressure. The time of contact of the form with the heatedprinting medium film thereon, or dwell time, against the stock can varyfrom a very small fraction of a second up to several seconds. However,for commercial use, it is preferred that this dwell time be not more icethan about one second. At the end of the dwell time when the form iswithdrawn from the stock it will be found that the dry medium film hasbeen transferred completely from the form to the stock. This is truewhether the form is a smooth polished surface or has a rough surfacesuch as is produced by sand blasting.

The printing medium that can be used may be any of the heat set printinginks customarily used in the printing industry. By this is meant boththermosettin-g inks and thermoplastic inks that become dry to the touchon the printing form or die. Thus, where the ordinary type of printingis practiced, the medium may contain a vehicle including a solvent and afilm forming solid material and, optionally, a pigment or pigments. Thefilm forming material may be any of the ordinary resins and may containmodifying agents such as dryers and addition agents. Typical filmforming vehicles may contain resins such as cellulose esters (nitrate,acetate or butyrate), alkyd resins, urea-formaldehyde resins, melamineresins, aryl sulfoamide resins, rosin and its esters and soaps,coumaroneindene resins, vinyl and acrylic resins, and other resinsconventionally used in coating compositions. All of these and others arewell known in the printing industry and all are usable in compoundingthe printing medium such as inks usable in the methods of thisinvention.

The printing media that can be used in this invention can also containordinary solvents including ketones, ethers, esters, alcohols, etheralcohols, hydrocarbons, chlorinated hydrocarbons, nitroparafiins andothers. Other solvents may include furfural and esterified terpenes andothers. Again, such solvents and their use in the printing industry iswell known. For commercially practical printing media it is preferredthat the solvents used have a boiling point between about -450 F. Wherepigments are used in making the printing media usable in this inventionthese pigments may be any of those commercially used in the printingindustry to give the desired characteristics of color, opacity, body orconsistency and the like. Thus, the normal pigments are powderspossessing coloring or hiding properties and are capable of being mixedor ground with a vehicle to form a homogeneous mixture. As is customaryin the printing industry, certain pigments are more correctly designatedas extenders but are customarily included in the pigment class. All suchpigments and extenders are well known and widely used in the printingindustry.

As can be seen from the above discussion of the printing mediaingredients the media that are used in the method of this invention arethose customarily used in ordinary heat set printing. A full discussionof such printing inks and printing media is given in Printing and LithoInks by H. I. Wolfe, 5th edition, copyright 1957 by MacNair-Dorland Co.

The printing medium used in the method of this invention has somethermoplastic quality in the heated dry film when subjected to printingpressure. This property is possessed by heat set printing inks generallyin spite of the fact that the heated dry film is dry to the touch andcannot be smeared with finger pressure.

The printing method of this invention is not necessarily limited toprinting characters on paper or the like. Thus, the method of thisinvention can be employed for coating stock such as paper stock. In thecoating process the liquid coating material is applied to a heated formof large extent and dried on the form in the manner previouslydescribed. The heated dry film is then pressed on the stock underordinary printing pressure in the manner described, whereupon the filmis transferred completely from the form to the stock. Thus, wherever theword printing is used herein and in the claims, it is intended toinclude such coating processes.

The method of this invention is of course different from conventionalprinting processes wherein the printing medium or ink image dries orbegins to dry after it has been transferred to the printing stock andsubsequent to the completion of the printing operation. In the presentinvention, of course, the printing medium is dried on the form to thecondition where it feels dry to touching or rubbing before beingtransferred to the stock. In other words, the film of dry medium is notaffected by physical touch or rubbing or marking. It is a necessaryrequirement of the present invention that the printing medium be thuslydried on the form, and this is most conveniently done by applying themedium to the form that has previously been heated to a temperaturesuflicient to dry the coating medium thereon to produce the heated dryfilm having the above characteristics.

The present invention in which the printing medium is transferred in asubstantially dry state lends itself to embossing simultaneously withthe printing step because the dry impression is not subject to smearingor blurring of outline upon the stock, while the latter migrates intothe recesses of the type or engraving during the imposition of pressure.Instead, the ink image will conform to the movement of the stock withoutdetriment or dam age to the appearance, finish, or precision of imagedefinition.

This novel procedure of combining the printing and embossing steps notonly obviates difiiculties heretofore encountered in achievingregistration between printing and embossing but effects a great savingin printing and embossing dies. In other words, conventional printingtype and plates may be employed without requiring the use of speciallocking embossing dies.

The invention also lends itself to combining the steps of laminating andprinting when lamination of the stock is desired. In such a case thelamina, or the stock, may be coated with a temperature sensitiveadhesive and the stock and lamina brought together and superposed at thesame point at which the printing step is performed. The heated printingform is applied to the laminae, or vice versa, and simultaneouslyachieves the dual function of transferring the printing medium to thestock and adhering the laminae together by the transfer of heat from theform through the laminae to the heat sensitive coating. Thissimultaneous combination of dry laminating and printing steps has notheretofore been feasible with inks that require drying after transferthereof.

The printing medium as mentioned above may be dried on the form merelyby using a heated form preheated to the drying temperature. However, ifdesired, a hot air blast against and across the medium coated form mayalso be used to aid the drying. This, however, is not required. Thesurface of the form is preferably a white metal such as steel, zinc,aluminum, manganese, nickel, chromium and the like in order to aid inthe complete transfer of the dry medium film from the form to the stock.Non-white metals such as copper or brass can be used but a larger dwelltime is required. The form may be heated by any means desired andconventional equipment such as ink rollers and the like are used in thecustomary manner to deposit ink or other printing mediums on the form.

The stock to be imprinted may be paper (including coated paper),regenerated cellulose, paper board (including coated board), textiles(including coated textiles), sheets or fihns of synthetic or naturalresins or plastics, metal foils such as aluminum foil, various laminates(including paper-metal foil, plastic-paper, textileplastic, etc.) andthe like. One of the important advantages of the invention is that thestock need not be heated or preheated in the printing. Thus the stockimmediately before printing may be at room temperature.

Although the printing medium may consist only of a film forming materialand a solvent, particularly where the printing is a coating operation,the medium may also contain modifying ingredients such as a separatingcompound, preferably a parafiin, wax or fatty acid, although othercompounds of a waxy or oil character such as sili cones, soaps, or fattyacids and alkyl esters of fatty acids have been employed successfully.The function of such a separating compound is to act as a lubricant orreleasing agent to reduce the adhesion between the ink and the form sothat the dried ink medium separates from the form or printing plate andbecomes adhered to the stock. As long as the form is made from thematerials noted above, the affinity of the medium for the form willalways be less than its atfinity for the stock or the coating thereon.More accurately, the gums or resins in the ink which constitute theadhesive have a greater tendency to adhere to the coating on the stockby heat sealing or to the surface of paper, paper-board or any othertype of printable stock than to the form.

It is also possible to include in the inking medium a plasticizer suchas dimethyl phthalate to cause plastic flow of the dried ink during theprinting step. Dimethyl phthalate also has separating properties, butits main function is to render the solid medium pliable and subject toplastic flow.

Example 1 One formula for an ink that has been tested with success is asfollows, with ingredients expressed in terms of percentage of totalweight:

The preferred form of cellulose acetate vehicle is as follows:

Percent Low viscosity cellulose acetate 9.2 Santolite MHP 8.9 Triacetin65.9 Ethyl lactate 21.0

The materials are adequately mixed and milled in the customary way forat least fifteen minutes on an open type mill. The carbon black andMilori Blue are of course included for color only and do not enter intothe present invention except insofar as they have characteristics commonto the remaining ingredients, in which case a change in their amountswill dictate changes in the amounts of other ingredients. The SantoliteMHP is a condensation product of formaldehyde and toluene sulfoamide.

The above medium may, for example, be employed to print on white patentcoated newsboard coated with cellulose acetate lacquer. The lacquerbegins to soften at about F. and if the temperature exceeds about 225 F.signs of deterioration appear and delamination and other defects result.Higher temperatures cause bubbling and extreme tackiness in the coating.A printing rate of one impression per second and an operatingtemperature of the ink of from 180 to 225 F. produces satisfactoryresults. Upon increasing the printing speed, a high temperature isdesirable and upon lowering the printing speed, a lower temperature canbe employed.

If it is desired to emboss the stock as well as print on it, it ismerely necessary to reduce the speed (to allow for necessary dwell time)and increase the printing pressure or substitute more resilient backingup materials for the stock.

If it is desirable, in addition, to incorporate a laminating step, it isnecessary to coat the laminae or the stock to which it is to be adheredwith a suitable conventional temperature sensitive heat sealing adhesivefor the temperature range involved. The lamina or tissue to be printedis then merely interposed between the other lamina and the form beforethe printing step is carried out.

From the above description it will be seen that the present inventiondiffers most radically from prior art methods of printing in that theink is dried before imprinting on the stock occurs. Although the mediumis transferred in a solid state to the stock, it is plastic and pliable.

Inasmuch as printing by the present invention takes place in a dry statewithout absorption of the printing medium into the body of the stock,greater economy is effected than has heretofore been possible becauseall of the ink is efiiciently employed in creating an image and none islost by absorption.

Because of the fact that no drying is required after the printing steptakes place, different colors may be added in rapid successionregardless of the type of stock employed. In other words, it is nevernecessary to slow down the printing operation to permit drying.

Another advantage of complete transfer printing with a dried ink mediumis that it is not necessary to resort to many different kinds of inksfor the infinite variety of stocks available for printing. In fact,utilization of complete transfer dry printing can result instandardization of compositions so that a universal composition can beemployed for practically every purpose of letter press printing.

It will also be apparent that a change-over from one type of stock toanother can be successfully accomplished merely by adjustment of theform temperature.

The simple adjustment of form temperature also permits variation in thefinish of prints, whether mat, lustrous or of an intermediate degree.For example, when printing from a tform surface that has been brought toa high polish, the result will be prints of the same glossy finish. Bymerely adjusting the temperature to a somewhat lower level, a mat finishmay be obtained. This is due to the fact that complete transfer printingemploys the technique of press polishing.

The present invention contemplates not only complete transfer printingand embossing by dried ink media, but also the combination of suchprinting with the step of lamination as described above.

The process by which drying of the ink medium is effected is notrestricted to evaporation as it is obvious that the same result may beachieved by evaporation, oxidation, polymerization, 'gelation, etc.

Although complete transfer dry printing finds its greatest applicationin use with type or plate forms, it is obvious that it may be employedfor coating the stock through the use of a smooth form.

In addition, since the transferred ink medium has heat sealingcharacteristics, the printed stock may be coated with a thin film ofpaper or the like that may be adherently secured to the printed stockwithout the addition of heat sealing material.

In the above Example 1 and in the following examples the ink was appliedto a printing form that had been heated to a temperature near theboiling point of the solvent and permitted to stand until the inkcoating had formed a film that was dry to the touch. The heated formwith the dried film thereon was then pressed against the paper stock forabout one second. This caused the film to be transferred from the formto the paper stock.

The following examples present different ink formulations that were usedin the above process.

Example 2 The ink consisted of 100 grams of vehicle, grams of finelydivided carbon black and 3 grarns of Milori Blue. The vehicle was madeup of of half-second viscosity cellulose butyrate and 80% carbitolacetate boiling at 248 C. All percentages used herein are by weight.

Example 3 The formulation here was made up of 100 grams of the vehicleof Example 2 and 100 grams of titanium dioxide.

Example 4 The ink consisted of 100 grams of vehicle, 10 grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of 15%3-second cellulose acetate and ethyl lactate boiling at 154.5 C.

Example 5 The formulation was made of grams of the vehicle of Example 6,10 grams of carbon (Bead Black) and 3 grams of Milori Blue.

Example 8 The formulation was made up of 100 grams of the vehicle ofExample 6 and 100 grams of titanium dioxide.

Example 9 The formulation was made up of 100 grams of the vehicle ofExample 6 and 100 grams of gold.

Example 10 The fiormulation was made up of 66.6 grams of the vehicle ofExample 6 and 33.3 grams of titanium dioxide.

Example 11 The formulation was made up of 260 grams of the vehicle ofExample 6 and 100 grams of Chrome Yellow.

Example 12 The formulation was made up of 200 grams of the vehicle ofExample 6 and 50 grams of Inon Blue.

Example 13 The formulation was made up of 100 grams of the vehicle ofExample 6 and 25 grams of gold.

Example 14 The ink consisted of 100 grams of vehicle, 10 grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of 15 3-secondcellulose acetate and 85% carbitol acetate boiling at 217 C.

Example 15 The ink consisted of 100 grams of vehicle, 10 grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of 25%half-second cellulose butyrate and 75% diac'etone alcohol boiling at 169C.

Example 16 The formulation was made up of 100 grams of the velricle, 10grams of carbon black and 3 grams of Milori Blue. The vehicle was madeup of 25% half-second cellulose butyrate and 75% butyl lactate boilingat 188 C.

Example 17 The ink consisted of 100 grams of vehicle, 10 grams of carbon:black and 3 grams of Milori Blue. The vehicle was made up of 25%half-second cellulose butyrate and 75 butyl cellulose acetate boiling at191.6 C.

Example 18 The ink consisted of 100 grams of vehicle, 10 grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of 25half-second cellulose butyrate and 75% DM Dowanol 16 (a polyglycolether) boiling at 194.1 C.

Example 19 The ink consisted of 100 grams of vehicle, grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of 25%half-second cellulose butyrate and 75% Ansol Ether #161 boiling at 216C.

Example 20 The ink consisted of 100 grams of vehicle, 10 grams of carbonblack and 3 grams of Milori Blue. The vehicle was made up of ethylcellulose and 75% carbitol acetate boiling at 217 C.

Example 21 The ink consisted of 67% vehicle (Heatset Varnish I), 18%carbon black, 5% Iron Blue and 10% Petroleum Solvent. The vehicle wasmade up of zincated rosin and 50% Petroleum Solvent which has a boilingrange of 475550 F. and has a KB volume between 20 and 30.

Example 22 The ink consisted of 70% vehicle (Heatset Varnish II), 18%carbon black, 3% Victoria Blue and 9% Petrolum Solvent II. The vehiclewas made up of 50% Pentalyn K (pentaerythritol rosin ester) (HerculesPowder Co.) and 50% Petroleum Solvent II which has a boiling range of425-500 F. and a KB volume between 20 and 30.

The printing medium that is applied to the form or die is preferably athick and viscous paste. This has two advantages, first, in thiscondition there is less solvent to be driven by the heat from the formand, second, an excess amount of solvent is avoided that can cause afilm to break on the form and give an imperfect impression.

The printing medium used in this invention may contain any thermoplasticor thermosetting film former that will result in a continuous film onthe form or die and that is dry to the touch. The film former must alsoflow under the pressure and temperature conditions of the printing step.The solvent used must be one that will dissolve the film former and thatcan be driven off by the heat of the form in a reasonable time.

The set time or the time that the printing medium remains on the form ordie is important. Thus, it should be sufficiently short so that theprinting can be done fiiciently so far as time is concerned yet must belong enough so that the film on the form is dry to the touch but isplastic under the pressures and temperatures of printing. The set timewhich can be determined quite easily empirically by anyone skilled inthe art is determined by a number of factors including the amount ofsolvent used, the thickness of the desired film and the drying of: thefilm so that an adequate transfer from the form to the stock isachieved.

The dwell time or the time the form or die is pressed against the stockcan also be determined quite easily empirically by those skilled in theart. The dwell time is of course long enough to transfer the film fromthe form or die to the stock.

In typical conditions of practicing the invention by using the printingmedium or ink of Example 2, the die temperature was 290 F. with theresult that the set tim varied between 3 and 5 seconds for mostefficient printing and the dwell time between 2 and 15 seconds. Withinthese ranges excellent results were produced with a set time of 1%.seconds and a dwell time of 3 seconds when the die temperature was 315F. As is obvious, the set time and dwell time may be decreased byraising the die temperature and increased by lowering the dietemperature. Under conditions of relatively high die temperature the settime has been reduced safely to about ,64 second while the dwell timehas been reduced to about 0.2 second.

Having described my invention as related to the embodiments set outherein, it is my intention that the invcntion be not limited by any ofthe details of description, unless otherwise specified, but rather beconstrued broadly within its spirit and scope as set out in theaccompanying claims.

I claim:

1. The method of letter press printing, comprising: applying a heatdriable liquid printing medium to a printing form; heating said mediumon the form for not more than about six seconds at a temperaturesuflicient to dry the medium to the touch on the form; and applying theheated medium while said medium is still hot to a stock that issubstantially at room temperature by pressing the form and hot mediumagainst the stock, said method resulting in the complete transfer of thedry hot medium from the form to the room temperature stock.

2. The method of claim 1 wherein said pressing of the form to the stockis for not more than about one second.

3. The method of letter press printing, comprising: applying a heatdriable liquid printing medium to a printing form previously heated to atemperature sufiicient to dry the medium to the touch on the form in aperiod of not more than about six seconds; maintaining the medium on theform for not more than said period to thusly dry the medium; andapplying the heated medium while said medium is still hot to a stockthat is substantially at room temperature by pressing the form and hotmedium against the stock, said method resulting in the complete transferof the dry hot medium from the form to the room temperature stock.

4. The method of letter press printing, comprising: applying a heatdriable liquid printing medium to a white metal printing form previouslyheated to a temperature sufiicient to dry the medium to the touch on theform in a period of not more than about six seconds; maintaining themedium on the form for not more than said period to thusly dry themedium; and applying the heated medium while said medium is still hot toa stock that is substantially at room temperature by pressing the formand hot medium against the stock, said method resulting in the completetransfer of the dry hot medium from the form to the room temperaturestock.

References Cited in the file of this patent UNITED STATES PATENTS2,587,594 Chavannes et al. Mar. 4, 1952 2,594,290 Chavannes Apr. 29,1952 2,858,232 Hushebeck et al. Oct. 28, 1958

1. THE METHOD OF LETTER PRESS PRINTING, COMPRISING: APPLYING A HEATDRIABLE LIQUID PRINTING MEDIUM TO A PRINTING FORM; HEATING SAID MEDIUMON THE FORM FOR NOT MORE THAN ABOUT SIX SECONDS AT A TEMPARATURESUFFICIENT TO DRY THE MEDIUM TO THE TOUCH ON THE FORM; AND APPLYING THEHEATED MEDIUM WHILE SAID MEDIUM IS STILL HOT TO A STOCK THAT ISSUBSTANTIALLY AT ROOM TEMPARATURE BY PRESSING THE FORM AND HOT MEDIUMAGAINST THE STOCK, SAID METHOD RESULTING IN THE COMPLETE TRANSFER OF THEDRY HOT MEDIUM FROM THE FORM TO THE ROOM TEMPERATURE STOCK.